Urinary incontinence (UI) affects many older women and greatly reduces quality of life. In the U.S., the most common type of UI in older adults is urgency UI and mixed-type UI. The most common type of medication used for urgency and mixed UI is an antimuscarinic drug. However, most patients on UI medications do not become completely dry and medications are often discontinued due to costs, negative side effects, or perceived inefficacy. Clearly, more efficacious treatments for UI are urgently needed. Evidence emerging from epidemiologic and clinical cohort studies indicates that lower vitamin D levels are associated with increased risk for UI suggesting that vitamin D may have a role in maintaining continence in women. Because the potential benefits of vitamin D may extend to several organ systems, it is quite possible that vitamin D may maintain continence by supporting skeletal muscle strength and normal detrusor activity. In the proposed study, we hypothesize that adequate vitamin D supplementation (raising serum levels to 30 ng/mL or above) will improve UI symptoms in older women with vitamin D deficiency (25(OH)D serum levels less than 20 ng/mL). The primary aim of the proposed double-blind, randomized, placebo-controlled pilot trial is to estimate the effect size of weekly vitamin D supplementation in older women with UI and vitamin D deficiency. The second aim is to evaluate if improving serum 25(OH)D levels affect other urinary and bowel symptoms. The third aim is to identify potential mechanisms that may contribute to improved UI symptoms in a subgroup of women, including increased pelvic floor skeletal muscle strength, decreased detrusor muscle over activity, improved mobility, and inflammatory urinary biomarkers. Post-menopausal women with vitamin D deficiency (n=100) will be recruited and randomized to receive weekly oral placebo or 50,000 IU vitamin D3 (cholecalciferol) for 12 weeks. Our treatment regimen is intended to achieve serum 25(OH)D levels of 30 ng/mL or above. Changes in UI-episodes will be assessed by 7-day bladder diary and other validated measures of urinary and bowel symptoms administered at baseline and after 12-weeks of intervention. Serum calcium and 25(OH)D levels will be monitored at: baseline, 6-week visit, and the end of 12 weeks of the intervention. Urodynamic (done in 50% of the study group), an assessment of pelvic floor strength, urinary collection for further testing, and mobility will be performed at baseline and 12-weeks.The expected outcomes will provide new knowledge regarding the impact of vitamin D supplementation on UI symptom improvement and inform a larger, randomized controlled clinical trial involving vitamin D supplementation.